A number of sensors and methods for determining at least one property of a measuring gas in a measuring gas space are available. In principle, this may involve arbitrary physical and/or chemical properties of the gas, whereby one or multiple properties may be detected. The present invention is described below in particular with reference to a qualitative and/or quantitative detection of a gas component of the gas, in particular with reference to a detection of an oxygen content in the gas. The oxygen content may be detected, for example, in the form of a partial pressure and/or in the form of a percentage. Alternatively or in addition, other properties of the gas may also be detected, such as the temperature of the gas, for example.
Such sensors may, for example, also be designed as so-called lambda sensors, as are described for example, in Konrad Reif (publisher): Sensoren im Kraftfahrzeug, 1st edition, 2010, pp. 160-165. With broadband and binary lambda sensors, in particular with planar broadband and binary lambda sensors, it is possible for example to determine the oxygen concentration in the exhaust gas at one point or in a large area, and thereby deduce the air-fuel ratio in the combustion chamber. Alternatively, the sensor may also be designed as a finger-type sensor. The air ratio λ describes this air-fuel ratio.
Sensors of this type normally have a housing which includes a housing opening through which the connection cables are led out, and a sealing body situated in the housing opening through which the connection cables extend. The sealing body is a stopper made of a homogenous elastomeric mass through which the connection cables are guided and which is subsequently caulked in a section of the housing designed as a metal sleeve. This is described, for example, in European Patent No. EP 2 192 403 A1. Heavy demands in terms of temperature and water and gas tightness are placed on such sensors and in particular on the cable outlet. To adjust the elastic properties which result in an improved processing and improved sealing behavior, plasticizers are added to the elastomer and homogenously distributed in the elastomeric mass during the manufacture of the sealing body.
Despite the numerous advantages of the conventional sensors, they still have potential for improvement. Thus, for example, a high proportion of plasticizers in the elastomeric mass creates a high elasticity, good processability in new condition, good sealing capability in particular in the area of the grommet, but also increased material discharge during thermal aging with accompanying shrinkage and embrittlement. This may result in the formation of critical leakage paths in the cable outlet of the sensor. Conversely, a lower proportion of plasticizers in the elastomeric mass leads to poorer processability and poorer sealing capabilities, but to improved aging behavior, since under thermal load only few volatile organic components are discharged with correspondingly little change in the properties of the sealing body.